The quest for K-d


Although the importance of kaonic deuterium X-ray spectroscopy has been well recognized, for more than 30 years (Richard Dalitz), no experimental results have yet been obtained due to the difficulty of the X-ray measurement.

“The necessity to perform measurements of the kaonic deuterium ground state observables is justified by the fact that, unlike the case of pionic atoms, the measurement of only the kaonic hydrogen spectrum does not allow - even in principle - to extract independently both s-wave K-nucleon scattering lengths a0 and a1", quoting from U.-G. Meißner.

The kaonic deuterium X-ray measurement represents the most important experimental information missing in the field of the low-energy antikaon-nucleon interactions today.

The kaonic hydrogen and deuterium data will also be indispensable when applying unitarised chiral perturbation theory to account for the L(1405) resonance in kaon-hadronic systems in nuclear matter.

For the precision X-ray measurement we plan to use new SDD chips, which were developed in collaboration with Fondazione Bruno Kessler – FBK and Politecnico di Milano in Italy.

Monolithic arrays with 9 detector segments with a total area of 5.76 cm2 are ideally suited for the proposed experiment. For these SDDs, special preamplifier chips (CUBE), were developed

For example the cryogenic target cell for J-PARC will be made of a 75μm Kapton body with a diameter of 65 mm and a length of 160 mm, with reinforcement structure made out of aluminium. The working temperature of the target cell is around 25 K with a maximum pressure of 0.35 MPa. With these parameters, a gas density of 5% liquid deuterium density (LDD) will be achievable. Finally, 48 monolithic SDD arrays will be structured close together around the target, with a total area of 246 cm2 containing 380 readout channels.

Simulated kaonic deuterium x-ray spectrum, assuming a 30 kW beam power, 100 shifts of data taking and a detector area of 246 cm2. Demanding an appropriate K- signal on the beam counter after the degrader and using additionally a vertex cut (fiducial volume 5 mm off the walls) as well as the charged particle veto for tracks passing SDDs.

Fitting a set of simulated data, we extracted the shift and width with a precision of 60 eV and 140 eV, respectively, which is comparable with the SIDDHARTA result of K-p.